There is a very small percentage of ADHD patients who have food sensitivities. Within that small percentage, there is a subgroup who are sensitive to red dye. For those individuals, avoiding red dye will make a significant difference in their symptoms.

My son who is almost 8 acts soooo strange when he has red dye 40. He gets this really wierd look on his face with a devilish grin and has to touch and pester everyone. He igores everything we say and he purposely pulls things apart.
We had him off red dye at home and once in a while he would act the same way so I thought it was not the red dye. I then found out the school serves strawberry milk every once in awhile. Which happened to be on the days he acted bizarre.
It has been a fairly quiet summer since I have full control over what he eats.

Actually Red Dye allergies are very common. I know 8 people with the allergy. My 7 year old daughter has it, and if she eats anything with red dye in it she goes from the sweet, help with everything, manners, minds me child, to this hell child that you can't make do anything and standing still isn't optional. Like two different people, split personality